Drilling oil and geothermal wells requires the use of drilling muds and well cements. These materials are especially designed for their properties at elevated temperatures and pressures. For development and testing of drilling muds and well cements, pressure vessels are required to simulate the down hole conditions. Pressurized consistometers for measuring thickening times and other properties already exist. With them, samples are tested in a rotating slurry cup with a stationary internal paddle. The consistency of the sample is measured as a function of the time under carefully controlled conditions of increasing temperature and pressure. In fact, standardized equipment and procedures are described in the Specification for Materials and Testing for Well Cements issued by The American Petroleum Institute (January 1982). Typically pressurized consistometers have been designed for a working pressure of 25,000 psi at a maximum temperature of 400.degree. F. The consistometer has consisted of a cup (for holding the well cement to be tested), a drive for rotating the cup at a constant speed (usually 150 rpm), and a paddle extending into the container which paddle is associated with a torque measuring transducer. Typically, the drive for rotating the container (or slurry cup as it is often called) passes through the vessel bottom through a high pressure packing. The torque measuring transducer has been positioned within the vessel in the form of a rotation detecting potentiometer and a standardized torsion spring. Electrical leads from the potentiometer pass through the top sides of the vessel. The vessel interior has been heated by electrical heating elements and pressurized by a hydraulic system (the specimen cup has a diaphragm over the top which substantially separates the pressurizing oil from the cement specimen being tested). Recently, packings through which the cup is driven have been replaced by permanent magnet drives.
Because deeper and deeper bores are being drilled and because of the increasing activity in the area of geothermal wells which bores are hotter, higher pressures (say 40,000 psi) and higher temperatures (say, 750.degree. F.) are being encountered. Thus better equipment for testing materials (muds and cements) at higher temperatures and pressures is required. The thermal performances is not simply a matter of maximum temperature but also a heating rate. Thus, increased heating rates in the range of 10.degree. F. per minute are sought.